All ammo in the currently released a critboost of 2. It's just not moddable. In all of this, most of these formulas are probably out for the next version. Negative critboosts act like zero.
As far as I could tell digging around, heat/cold/burn damage are all the same except for where they come from and what text they produce.
Speed controls how many attacks you get, as it controls the rate of every other conscious act you are allowed to take. If a creature is swimming, it'll use their swim speed for everything. The speed split is one of the most important parts of the combat arc, and it'll have impacts everywhere.
Speed has a few pages of modifiers... here, higher is slower. magma swimming is x2, swim skill starts modifying speed at level 2, and from 2 to 15 it multiplies by 19/20 to 6/20. If you are not swimming but just walking through the liquid due to lack of skill, it adds 150*depth to your speed for water and 300*depth to your speed for magma. babies get +3000. each level of exertion adds 200. gutted +2000. naus/wind/stun +1000 each. pain w/out trance +1000. each level of hunger thirst sleep +100. leading an animal 1000. zombie 5000 ground 2000 sneaking if not a trained animal 2000 - sneak*100 where sneak is the skill level up to 20. paralyze level*100. web level * 100. every agility level up to 5 takes off 10%. if you are not on the ground and your race has >=3 limbs and you don't have the use of 1+ of them, then if positive add the number (500*(bad limbs)/(total-total/2-1)) - toughness*100. melancholy mood + 8000.
finally the inventory speed: add up all the weights, but if armor skill>=2 only count armor as (15-ask)/16 -- so legendary armor users aren't affected at all by armor. then take 2000 + strength*1000. if the weight is greater than this, take the difference. speed + (diff/2+1)
speed capped at 9999.